Optimisation of in-service performance of boiler steels by modelling high-temperature corrosion



The main objective of the EU OPTICORR project is the optimisation of in-service performance of boiler steels by modelling high-temperature corrosion, the development of a life-cycle approach (LCA) for the materials in energy production, particularly for the steels used in waste incinerators and co-fired boiler plants. The expected benefits of this approach for safe and cost effective energy production are:

- control and optimisation of in-service performance of boiler materials,

- understanding of high-temperature corrosion and oxidation mechanisms under service conditions,

- improvement of reliability to prevent the failure of components and plant accidents and

- expanding the limits of boiler plant materials by corrosion simulations for flexible plant operation conditions (steel, fuel, temperature etc.).

The technical aim of the EU OPTICORR project is the development of modelling tools for high-temperature oxidation and corrosion specifically in boiler conditions with HCl- and SO2-containing combustion gases and Cl-containing salts.

The work necessitates thermodynamic data collection and processing. For development and modelling, knowledge about the corrosion mechanisms and exact data are needed. The kinetics of high-temperature oxidation and corrosion are determined from laboratory thermo-gravimetric tests (TG) and multi-sample exposure tests. The materials studied are typical boiler tubes and fin-steels: ferritic alloys, the austenitic steel T347 and the Ni-based alloy Inconel 625. The exposure gases are dry air, air with 15 vol-% H2O, and with 2000 ppm HCl and 200 ppm SO2. The salt deposits used are based on KCl-ZnCl2 and Ca, Na, K, Pb, Zn-sulfates. The test temperatures for exposures with deposits are 320 and 420°C and, for gas exposures, 500 to 600°C.

At present the tools being developed are ChemSheet based programmes with a kinetic module and easy-to-use interface and a more sophisticated numerical finite-difference-based diffusion calculation programme, InCorr, developed for prediction of inward corrosion and internal corrosion.

The development of modelling tools for oxidation and high-temperature corrosion was started with thermodynamic data collection for relevant systems and thermodynamic mappings. Further, there are needs to develop the simulation model and tool for salt-induced hot corrosion based on the ChemSheet approach. Also, the work on modelling and simulating with the InCorr kinetic modelling tool will be continued to demonstrate the use of the tool for various steels and alloys in defined combustion environments.